Introduction and Problems
There are many situations where the mixing of hot and cold liquids is effected via a single lever mixing valve or mixer. Some may contain a cartridge, others may not. Some may have a movable distributing member which may loosely be termed “spherical”, although only a portion would have a spherical surface. Other movable distributing members may be loosely termed “cylindrical” or “flat”. “Flat” movable distributing members are usually ceramic, usually disc-shaped, and operate in conjunction with a stationary distributing member which is also ceramic and flat as opposed to cupped. Regardless of the form of the distributing members this type of mixer can allow dangerously hot liquid to be fed from it. In the typical situation where the liquids are water in a domestic supply, there is a minimum desirable temperature of any stored hot water fed to such a mixer. With water stored in bulk the storage temperature should exceed 61° C. to avoid contamination with Legionnaires disease. The problem is that water even at 61° C. is at too high a temperature for the human body to contact safely for long. Where the water is not stored but heated in response to draw-off demand there may be no problem if the heat input is restricted so the inflow is supplied at a satisfactory lower temperature—that is until the heat control malfunctions. Similarly while it is well known to have a tempering valve on a bulk supply of hot water so that the hot feed from it is diluted with cold water to give a mixed flow with a temperature lower than the storage temperature, that too may only be satisfactory while the tempering valve does not malfunction and while the heat input control also does not malfunction. A typical problem could be loss of cold water pressure.
How Prior Art 3-Port Single Lever Mixing Valves Work—FIG. 1
In order to facilitate an understanding of how the device of the present invention differs from the prior art single lever mixing valves or cartridges incorporating movable distributing members and stationary distributing members discussion of a typical prior art ceramic disc-type construction now follows with reference to FIG. 1 which is entirely schematic.
A prior art single lever mixing valve has a stationary lower distributing member 1 with a flat upper sealing portion 2 and a movable upper distributing member 3 which has a flat lower sealing portion (not shown). The function of the distributing members is to progressively open and close two input feeds to and from a combined output flow and to keep the input feeds closed from each other when there is to be no output flow.
The movable and stationary distributing members are suitably supported in a body 4 which may be a cartridge body or the body of an entire valve. From suitable supply sources hot and cold liquids are separately fed through the body to separate hot and cold inlet ports such as 5,6 through the lower distributing member 1.
The upper distributing member 3 is able to be rotated to a degree (about 35°-100° is common in the prior art) about an axis such as A, or one parallel to it, which is substantially perpendicular to the plane of the flat sealing portion 2 of the lower distributing member 1, to control the proportions of hot and cold liquids passing through the ports; and also is able to be slid transversely across the lower distributing member 1 to control the flow rates; all the while the flat sealing portions, or parts thereof, maintaining sealing contact. In one position, or sometimes several positions, of the upper distributing member is there is complete shut-off of possible liquid flow out of the valve or cartridge. Sealing contact is provided by the trueness or flatness of the coacting sealing portions which are held pressed together by the pressure of the liquid feed trying to displace the stationary distributing member axially towards the movable distributing member which is restrained against axial movement. “O”-ring seals such as 7 and 9 allow slight axial movement of the stationary distributing member with respect to the body 4 while still maintaining relative sealing. Ports 5 and 6 pass right through the stationary distributing member and communicate with a mixing space 10, usually a cavity wholly contained within the movable distributing member, where mixing of hot and cold liquids occurs and thence the mixture flows out from the valve via port 8 which passes right through the stationary distributing member. The axis A would usually be upright on installation of the valve, with the movable distributing member above the stationary distributing member.
In the usual arrangement, at all times the mixing space and outlet would be in communication to some extent regardless of the lift position of the lever. But when the lever is fully depressed the mixing space is sealed off from the inlet ports 5,6.
The above description would encompass many of the known types of 3-port single lever mixing valves as commonly used for domestic hot and cold water regulation for baths, hand-basins and sink-basins.
Disadvantages of the Above Types of Valve and Solutions Required
The above types of valve may be quite adequate when used with a hot liquid supply whose flow ceases if the cold liquid flow ceases and whose temperature can never exceed a safe upper limit because of the use of a reliable tempering valve or similar on the bulk supply. Typically a mains pressure supplied hot water cylinder will cease to feed hot water if the cold mains pressure water supply to it stops.
However, the above type of valve has no means of limiting the maximum temperature of the liquid emerging from it and that is the problem the present is invention seeks to solve. The prior art valve could never be considered to be fail-safe but that is what is required.
The solution which the present invention seeks to provide is to supply a means whereby the mixer can internally impose an upper limit on the zo temperature of any liquid emerging from it. The means would preferably enable the upper limit to be changed by exchange or selection of a component so that the mixer could be used in any location in an installation even though different locations might have different upper limit requirements while having the same temperature of hot liquid input. It would preferably take the form of a cartridge able to be exchanged with an existing cartridge to convert an “unsafe” mixer to a “safe” one.
Temperature Sensing Devices
The exchangeable or selectable component of the device of the present invention is a temperature sensing device. The temperature sensing device must be capable of an externally sensible movement, such as a lengthwise expansion, when subjected to increasing temperature. It must move back on cooling. The housing or body of the temperature sensing device may be of any suitable shape but will usually be elongated and will usually be mostly cylindrical. The temperature sensing device may function rather like an hydraulic ram, with a piston which is movable in and out from the housing of the device (usually sealingly movable). However, the motive force in such a case is not hydraulic fluid but may arise, at least in part, from the volumetric change of a suitable flowable substance contained within the housing, when the substance is heated or cooled. Another means of providing motive force is the use of bimetallic discs within the housing, which cup on heating. The force so generated is used to move the piston either by direct pressure on it within the housing, or via a resilient means, such as a compression spring, within the housing, and there may be external resilient forces acting on the piston outside the housing. Thus heat elongation may be the result of direct pressure on the end of the piston inside a very conductive housing (eg a copper fluted housing) from an expanded flowable substance (usually a wax and a conductive medium such as copper particles) within the housing, expanding into the space it causes the piston to vacate. Such an expansion force might be partially countered by a resilient force, such as a compression spring within or outside the housing, which will serve to assist withdrawal of the piston back into the housing as the substance is cooled. A more recent development is the use of “shape memory” alloys containing nickel and titanium.
Another form of temperature sensing device might be a suitable flowable substance contained in a flexible bag constrained by a supporting, possibly upright cylindrical, grid to allow an upper or lower surface, or both, to move axially in response to temperature change. There is thus no piston or housing with such a temperature sensing device.
All types of temperature sensing device with any means of providing a sensible or detectable movement with a utilisable resultant motive force are intended to be within the scope of the present invention. The precise means causing the temperature sensing device to operate in the required fashion is not crucial. There may be many variants and performance characteristics from which those skilled in the art may select according to the functions required of the device. Some of the characteristics which will usually be important are the response time after a temperature change, the motive force capable of being developed, impedance to flow if a liquid is to flow through the device as opposed to around it and reproducibility of an extension at the same temperature including whether there is any hysteresis. The location of the temperature sensing portion of the temperature sensing device would be another criterion as would be the overall size.
Known Means of Avoiding the Disadvantages of 3-Port Mixers
The closest known prior art is U.S. Pat. No. 6,257,493 and others in its family.
The teaching of specification U.S. Pat. No. 6,257,493, however, provides no useful solution. Its teaching connects the outlet of a single lever mixing valve with the cold liquid inlet via a piston-type temperature sensing device. Only a mechanical seal, reliant on sustained spring biasing against the unbalanced liquid pressures, stops cold liquid leakage into the outlet. Such a construction would never be reliable in practice.